1. Field of the Invention
The present invention relates generally to continuous coating method and apparatus and, more particularly, to a modular ion-beam-assisted-deposition (IBAD) apparatus and method for the continuous coating of a wide range of materials, and products so made.
2. The Prior Art
Industry, in particular the steel industry, employs a great number of surface treatments and coatings for their products. The surface treatments and coatings are designed primarily to improve the products' wear, corrosion and/or oxidation resistance, and in some applications, their aesthetic appearance as well. In the steel industry, low carbon steels (steels with carbon content ranging from about 0.002 to about 0.09 percent) constitute the majority of steels currently in production for continuous sheet material Most of these are flat products where the thickness of the sheet steel is from about 0.3 mm to about 2.0 mm and is typically produced as a cold rolled steel. Such flat steel sheet products are required in large volumes, inter alia, by the automotive industry, where corrosion and oxidation resistance are of principal concern. Zinc and cadmium coatings applied to one or both sides of the flat steel sheets are preferred to improve their corrosion and/or oxidation resistance.
Presently, such coatings to flat steel sheets are applied either by bath plating or electroplating techniques. They are high volume, low cost processes. Changing from zinc coating to another type of coating presents considerable difficulties and expense, however. Additionally, there is currently significant governmental and/or environmental market pressure to switch, wherever possible, to alternate methods of coating flat steel sheets with materials. First, toxic waste generated by the bath and electroplating techniques should be eliminated or at least substantially reduced. Second, there is a need for higher performance coatings, particularly regarding qualities of adhesion, microstructure, uniformity and reproducibility of the coatings as between successive batches. Third, there is a need to improve production efficiency by eliminating or reducing waste, a characteristic of the bath and electroplating processes.
Another large area of utilization for flat steel sheet products in preferred thicknesses from about 0.1 mm to about 0.3 mm include their use as cans and for food packagings. For use in cans, for instance, the steel sheet first is dip-plated, preferably with a tin coating in the range of 2 to 4 microns and then a polymer coating is applied thereto.
Aside from the above "flat" products, steel products requiring coatings include "long" products formed in bar, rod or extrusion forms and comprise such items as I-beams, H-beams, railway extrusions and reinforcement rods used in construction. Then there are the low carbon steel wires and springs used as nuts, bolts, general wire, and various kinds of springs. Coatings thereto presently are generally applied by phosphidation or other conversion coating processes with or without also applying a polymer coating to anchor the phosphide coating, which has a tendency to flake off.
High carbon steels (with carbon content in excess of about 0.1 percent) are employed, inter alia, as tool steels for cutting, slicing, scoring, dicing, milling, and other mechining applications. Coatings such as, of titanium nitride and aluminum oxide, usually are applied with an adhesive layer to strengthen adhesion.
The deposition of boron nitride as well as other refractory nitride thin film coatings on various substrates by ion beam assisted deposition (IBAD) is already known. See R. J. Bricault et al., "Deposition of Boron Nitride Thin Films by Ion Beam Assisted Deposition," Nuclear Instruments & Methods in Physics Research B21, (1987) pp. 586-587; and T. G. Tetroult et al., "The Friction and Wear Behavior of Ion Beam Assisted Nitride Coatings,"Mat. Res. Soc. Symp. Proc., vol 128 (1989), pg. 439.
Ion implantation has been employed in the preparation of phosphor (U.S. Pat. No. 4,039,699), in the deposition of ionized clusters on substrates (U.S Pat. No. 4,152,478), and in the method of coating with a stoichiometric compound (U.S. Pat. No. 4,281,029). The common assignee herein, Spire Corporation of Bedford, Mass., has been one of the pioneers in working with ion beams. For instance, among thers it has patented an ion beam coating apparatus (U.S. Pat. No. 4,440,108), a plasma ion deposition process (U.S. Pat. No. 4,443,488), a process for preventing surface discoloration in orthopaedic implants (U.S. Pat. No. 4,693,760), a process for the ion implantation of plastics (U.S. Pat. No. 4,743,493), a process of treating metal alloys to inhibit corrosion (U.S. Pat. No. 4,743,308), a sputter-enhanced ion implantation process (U.S. Pat. No. 4,855,026), and a method and apparatus for ion implanting spherical surfaces (U.S. Pat. No. 4,872,922). In each of these methods, the apparatus employed has been one capable for batch-processing only. A continuous on-line coating apparatus employing ion beam technology would speed up processing and reduce costs, thereby provide access to high volume, large area products.